Error: Unresolved external symbol error in C++

Question

The compilation issue is caused by the global variable [ All_Sockets ], here is the minimal example

main.cpp

#include <winsock2.h>
#include <windows.h>
#include <vector>
#include "global.h"


int main() {

    std::vector<SOCKET> All_Sockets(10, INVALID_SOCKET);    // definition of global var

    getchar();
    return 1;
}

global.h

#pragma once
#include <vector>
#include <Windows.h>

extern std::vector<SOCKET> All_Sockets;      // declaration of global variable

file1.cpp

#include "global.h"
#include <windows.h>

void ftn1(){
    int i = 2;
    SOCKET Client_socket = All_Sockets[i];      // usage of global var
}

I'm building this project in visual studio and the following linking error occurs

1>file1.obj : error LNK2001: unresolved external symbol "class std::vector<unsigned int,class std::allocator<unsigned int> > All_Sockets"

secuman · Accepted Answer · 2021-09-01 09:27:11Z

2

You must define All_Sockets as global variable. Currently, All_Sockets is defined as local variable, so All_Sockets must be defined above main function.

std::vector<SOCKET> All_Sockets(10, INVALID_SOCKET);    // definition of global var

int main() {
    getchar();
    return 1;
}

answered Sep 1, 2021 at 9:27

secuman

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1 Comment

user260854 Over a year ago

Oh, I thought only the declaration should be global. thanks for the reply :)

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